Patent Grant
11270633
This disclosure relates generally to driving light emitting diodes (LEDs) of a display device, and more specifically to controlling skew of LED zone driving times in the display device with distributed driver circuits.
LEDs are used in many electronic display devices, such as televisions, computer monitors, laptop computers, tablets, smartphones, projection systems, and head-mounted devices. Modern displays may include very large numbers of individual LEDs that may be arranged in rows and columns in a display area. In order to drive each LED, a power supply supplying current to all of the LEDs must meet challenging transient response requirements.
Embodiments relate to a display device that drives light emitting diode (LED) zones according to a skewed pulse width modulation (PWM) dimming schema for controlling LED zone driving times. The display device includes an array of driver circuits and LED zones distributed in a display area. The LED zones include one or more LEDs. The display device further includes a control circuit to generate and send dimming signals to the array of driver circuits to control respective duty cycles for driving the LED zones during a frame. Each driver circuit receives the respective duty cycles for the frame at a first time and receives an update signal at a second time. Each driver circuit drives one LED zone according to the respective duty cycles of the dimming signals in response to the update signal. Different groups of driver circuits start driving their respective LED zones at different respective offset times during the frame.
Embodiments also relate to an integrated LED and driver circuit for a display device that operates according to the skewed PWM dimming schema for controlling LED zone driving times. The integrated LED and driver circuit for a display device includes a substrate. The integrated LED and driver circuit further includes a LED zone comprising one or more LEDs in a LED layer over the substrate. The LEDs generate light in response to a driver current. The integrated LED and driver circuit further includes a driver circuit over the substrate in a driver circuit layer and integrated into a common package with the LED zone. The driver circuit obtains a duty cycle for a frame at a first time and receives an update signal at a second time. The driver circuit drives the LED zone according to the duty cycle in response to the update signal.
Embodiments also relate to a method for operating a display device for driving an LED zone in a controlled manner. A control circuit transmits dimming signals to an array of driver circuits distributed in a display area of the display device at a first time. The dimming signals control respective duty cycles for driving an array of LED zones in the display area during a frame. The control circuit transmits one or more update signals to the driver circuits at a second time. A driver circuit in the array of driver circuits drives a LED zone of the array of LED zones. The driver circuits drive the respective LED zones according to the respective duty cycles of the dimming signals in response to the one or more update signals. Different groups of driver circuits start driving their respective LED zones at different respective offset times during the frame.
The teachings of the embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.
The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the inventive aspect matter.
The Figures (FIGs.) and the following description relate to the preferred embodiments of the present invention by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of the present disclosure.
Reference will now be made in detail to several embodiments of the present invention(s), examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
The device array 110 includes distributed zone integrated circuits (ICs) 130. At least some of the zone ICs 130 include an LED zone 140 and a driver circuit 150 that drives the LED zone 140. In some embodiments, other zone ICs 130 may include sensor devices. In other cases, the zone ICs 130 may include driver circuits 150 that are coupled to external LED zones 140. The device array 110 may be arranged in groups (e.g., rows or columns). Each group of zone ICs 130 may share common control and power lines for the driver circuits 150, LED zones 140, or both.
As will be described in further detail below, the zone ICs 130 may be physically structured such that the LED zones 140 are stacked over the driver circuits 150. In other words, an array of LED zones 140 are arranged in a first x-y plane and an array of driver circuits 150 are arranged in a second x-y plane parallel to the first x-y plane. In one configuration, each LED zone 140 is stacked over (i.e., in the z direction) the corresponding driver circuit 150 that drives it. Furthermore, the LED zone 140 and the driver circuit 150 of a zone IC 130 may be integrated on the same substrate and in a same package as further described in
The LED zones 140 each comprise one or more LEDs that each generate light that has a brightness dependent on respective driver currents provided by the corresponding driver circuits 150. In an LCD display, an LED zone 140 may comprise one or more LEDs that provide backlighting for a backlighting zone, which may include a one-dimensional or two-dimensional array of pixels. In an LED display, an LED zone 140 may comprise one or more LEDs corresponding to a single pixel of the display device 100 or may comprise a one-dimensional array or two-dimensional array of LEDs corresponding to an array of pixels (e.g., one or more columns or rows). For example, in one embodiment, the LED zone 140 may comprise one or more groups of red, green, and blue LEDs that each correspond to a sub-pixel of a pixel. In another embodiment, the LED zone 140 may comprise one or more groups of red, green, and blue LED strings that correspond to a column or partial column of sub-pixels or a row or partial row of sub-pixels. For example, an LED zone 140 may comprise a set of red sub-pixels, a set of green sub-pixels, or a set of blue sub-pixels.
The LEDs may be organic light emitting diodes (OLEDs), inorganic light emitting diodes (ILEDs), mini light emitting diodes (mini-LEDs) (e.g., having a size range between 100 to 300 micrometers), micro light emitting diodes (micro-LEDs) (e.g., having a size of less than 100 micrometers), white light emitting diodes (WLEDs), active-matrix OLEDs (AMOLEDs), transparent OLEDs (TOLEDs), or some other type of LEDs.
The driver circuits 150 drive the LED zones 140 by controlling the respective driver currents supplied to the LED zones 140 in response to driver control signals. In an embodiment, a driver circuit 150 controls a driver current supplied by a power supply (not shown) to control brightness of the LED zone 140 based on the driver control signals. For example, the driver circuits 150 may utilize a pulse width modulation (PWM) technique to control the brightness by modifying a duty cycle for each frame.
In some embodiments, the driver circuits 150 each drive multiple channels of a corresponding LED zone 140 that may each have separately controllable driver currents. For example, the driver circuit 150 may independently control LED currents corresponding to red, green, and blue channels of the LED zones 140.
The driver circuits 150 may be arranged in groups that share a common set of driver control lines. A group of driver circuits 150 can correspond to, for example, a row of driver circuits 150, a column of driver circuits 150, a partial row or partial column of driver circuits 150, or a block of adjacent driver circuits 150 that may span multiple rows or columns.
The control circuit 120 generates dimming signals as driver control signals according to image or video data. The dimming signals control the PWM on-times for each driver circuit 150 and controls a relative skew of the PWM on-times so that different driver circuits 150 or groups of driver circuits 150 turn on their corresponding LED zones 140 at different start times during each frame. The control circuit 120 provides the dimming signals to the driver circuits 150 for each image or video frame to control when each LED zone 140 turns on and to control their respective duty cycles. Different processes for controlling the relative skew of the PWM on-times of LED zones 140 are described in further detail in
In different embodiments, different connectivity configurations may be employed to couple the control circuit 120 to the zone ICs 130 for communicating the driver control signals. For example, in an embodiment, each group of zone ICs 130 is coupled by a shared parallel communication line that provides the driver control signals to the zone ICs 130 and targets different signals to different zone ICs 130 using unique addresses. The shared parallel communication line may comprise a dedicated communication line or may comprise a power communication line that both provides a supply voltage to the zone ICs 130 and includes digital data modulated on the supply voltage. In this embodiment, the zone ICs 130 may furthermore include serial connections between adjacent zone ICs 130 in a group and between the group of zone ICs 130 and the control circuit 120 to form a serial communication chain. The serial communication chain may be utilized to facilitate assignment of addresses to the zone ICs 130 at startup, may be used to communicate various commands to the zone ICs 130, and/or may be used to communicate readback data from the zone ICs 130 to the control circuit 120.
Alternatively, the control circuit 120 may include sets of control lines across multiple dimensions to facilitate communication of the driver control signals without addresses. Here, a group of zone ICs 130 along a first dimension (e.g., a row) may be selected based on a first shared control line coupled to all the zone ICs 130 in the group. Then the driver control signals may be communicated in parallel using a set of separate control lines that may be shared between zone ICs 130 along a second dimension (e.g., a column).
A control circuit 120 of the display device 100 provides 210 respective duty cycles to each individual driver circuit 150 for displaying a current image or video frame via a duty cycle signal. After all of the driver circuits 150 receive their respective duty cycles for the frame, the control circuit 120 sends 220 an update signal to a selected group of driver circuits 150 (e.g., a row). The update signal may be sent via a shared communication line for the group of driver circuits 150. The driver circuits 150 in the selected group each drive 230 their respective LED zones 140 according to the duty cycle information of their respective duty cycle signals responsive to the update signal. For example, each driver circuit 150 in the group begins driving (i.e., turning on) its corresponding LED zone 140 immediately after, or a fixed time after, the driver circuits 150 receive the update signal. The control circuit 120 determines 240 if all groups of driver circuits 150 have received a respective update signal for the current frame. If all groups of driver circuits 150 have not received a respective update signal, the control circuit 120 waits 250 a predefined time interval (e.g., an amount of time less than the image or video frame period) and sends 220 a respective update signal to the next group of driver circuits 150. The driver circuits 150 of the next group begin driving 230 their respective LED zones 140 according to duty cycle information of their respective duty cycle signals responsive to the update signal. This repeats for each group of driver circuits 150. If all groups of driver circuits 150 have received their respective update signals, the control circuit 120 waits 245 until the next frame time, and the process 200 repeats according to the dimming data for the next frame.
The duty cycle signals are sent to each of the driver circuits 150 of the display device 100 during a duty cycle control period 211 prior to or at the beginning of a frame.
Update signals (e.g., an update signal 221 for a first group of driver circuits 150, update signal 223 for a second group of driver circuits 150, update signal 225 for a third group of driver circuits 150, and update signal 227 for a fourth group of driver circuits 150) are asserted sequentially such that the update signal for each group of driver circuits 150 is delayed relative to the update signal for a previous group of driver circuits 150.
The driver circuits 150 in each group begin driving their respective LED zones 140 responsive to the update signals 221, 223, 225, 227 so that each group turns their respective LED zones 140 on at different start times. The composite driver current waveform 233 illustrates the combined driver currents being supplied to all of the LED zones 140 of the display device 100. In portion 260 of the waveform 233, the composite driver current gradually increases over time as each group of driver circuits 150 begins providing driver currents to their respective LED zone 140 responsive to the respective update signals. Each individual driver circuit 150 turns off its corresponding LED zone 140 after a drive time based on its programmed duty cycle for the current frame. By offsetting (or skewing) the update signals 221, 223, 225, 227, the display device 100 reduces the transient drive current for driving the LED zones 140 relative to an operating technique that instead turns on all LED zones 140 simultaneously.
The composite driver current waveform 380 illustrates the combined driver currents from all driver circuits 150 to their respective LED zones 140 of the display device 100. In portion 385 of the waveform 380, the composite driver current gradually increases over time as different groups of driver circuits 150 turn on their respective LED zone 140 based on the programmed offset times.
In some embodiments, the first process 200 and the second process 300 may be combined in the operation of a display device 100. Here, the control circuit 120 provides separate update signals to each group of driver circuits 150 and individual driver circuits 150 in the group turn on their respective LED zones 140 after a preprogrammed offset time.
In an example implementation, each driver circuit 150 may turn on their respective LED zone 140 such that the midpoint of the on-time (set by the duty cycle for the driver circuit) corresponds to the reference time. For example, if the reference time is set to a midpoint of the frame and a duty cycle for a driver circuit is set to 50%, the driver circuit 150 turns on its corresponding LED zone 140 after 25% of the frame time has passed, and turns off the LED zone 140 after 75% of the frame time has passed. In other embodiments, the driver circuits 150 may turn on the respective LED zones 140 so that the reference time occurs after a different fixed fraction of the on-time set by the duty cycle has passed that is not necessarily the midpoint. For example, the driver circuits 150 may turn on the respective LED zones 140 so that the reference time occurs after 25% of the on-time, after 75% of the on-time, or after any other programmed proportion. Furthermore, the reference time need not necessarily correspond to the midpoint of the frame time and may occur at any other preprogrammed time during the frame. In the case that the driver circuits 150 additionally receive a programmed offset time, the time at which the driver circuit 150 turns on the respected LED zone 140 may first be computed using the technique above and then adjusted by the programmed offset. The offset times may be positive to cause the midpoint (or other programmed point) of the on-time to lag the time indicated by the reference time in conjunction with the duty cycle, or the offset time may be negative to cause the midpoint (or other programmed point) of the on-time to precede the time indicated by the reference in conjunction with the duty cycle. In general, the time at which the LED zone 140 turns on may be computed as follows:
TON(i)=TRef−D(i)·FT·P+TOffset(i) (1)
where TON represents the time at which the LED zone i turns on relative to the start of the frame (or the update signal), TREF is the reference time relative to the start of the frame, D is the duty cycle for a specific driver circuit driving the LED zone i, FT is the duration of the frame, P is a position value between 0 and 1 indicating a fraction of the on-time set by the duty cycle that occurs prior to the reference time, and TOFFSET represents a programmed offset time associated with the driver circuit 150 driving the LED zone i. The steps 415, 420, 425 repeat for each frame.
In an embodiment, the offsets TOFFSET may be applied only in situations when the duty cycles for multiple driver circuits 150 are the same or very close to ensure that the driver circuits 150 still turn on their respective LED zones 140 at different times. For example, the control circuit 120 may detect when over a threshold number of driver circuits 150 are programmed to operate with coincident turn on times and cause the driver circuits 150 to operate according to programmed offsets in response. Alternatively, if a group of driver circuits 150 share a common control line, the driver circuits 150 may individually detect when at least a threshold number of other driver circuits 150 in the group are programmed with coincident turn on times and apply a programmed offset in response. Thus, in this embodiment, the turn on times are selectively skewed by the offset times dependent on the control data for that frame.
In a further embodiment, the update signals may be sent at different times for different groups (e.g., rows) of driver circuits 150. Each driver circuit 150 in a group may then operate according to the principles described above. In this embodiment, the total skew for a driver circuit 150 is dependent on both its group association (e.g., what row it is in) and its programmed or computed time at which the driver circuit 150 turns on the respective LED zone 140 relative to the timing of the update signal.
In a further embodiment, the control circuit 120 may detect when over a threshold number of driver circuits 150 are programmed to operate with coincident turn off times and cause the driver circuits 150 to operate according to programmed offsets in response to shift the respective turn on times in a manner that avoids the turn off times coinciding. Alternatively, if a group of driver circuits 150 share a common control line, the driver circuits 150 may individually detect when at least a threshold number of other driver circuits 150 in the group are programmed with coincident turn off times and apply a programmed offset in response to shift the respective turn on times in a manner that avoids the turn off times coinciding. Thus, in this embodiment, the turn off times are selectively skewed by the offset times dependent on the control data for that frame.
The composite driver current waveform 440 illustrates the combined driver currents being supplied from all driver circuits 150 to their respective LED zones 140 of the display device 100. In portion 445 of the waveform 440, the composite driver current gradually increases over time as different driver circuits 150 turn on their respective LED zone 140 so that the rate of transient current change is limited. Similarly, the composite driver current 440 indicates gradually decreasing current as different driver circuits turn off their respective LED zones 140 at different times.
The composite driver current waveform 470 illustrates the combined driver currents being supplied from all driver circuits 150 to their respective LED zones 140 of the display device 100. In portion 475 of the waveform 440, the composite driver current gradually increases over time as different driver circuits 150 turn on their respective LED zone 140. Similarly, the composite driver current 475 indicates gradually decreasing current as different driver circuits turn off their respective LED zones 140 at different times.
The composite driver current waveform 490 illustrates the combined driver currents being supplied from all driver circuits 150 to their respective LED zones 140 of the display device 100. In portion 495 of the waveform 490, the composite driver current gradually increases over time as different driver circuits 150 turn on their respective LED zone 140 at different times. Similarly, the composite driver current 490 indicates gradually decreasing current as different driver circuits turn off their respective LED zones 140 at different times.
In the embodiments of
The driver circuits 520 may operate in various modes including at least an addressing mode, a configuration mode, and an operational mode. During the addressing mode, the control circuit 510 initiates an addressing procedure to cause assignment of addresses to each of driver circuits 520. During the configuration and operational modes, the control circuit 510 transmits commands and data that may be targeted to specific driver circuits 520 based on their addresses. In the configuration mode, the control circuit 510 configures driver circuits 520 with one or more operating parameters (e.g., overcurrent thresholds, overvoltage thresholds, clock division ratios, and/or slew rate control). During the operational mode, the control circuit 510 provides control data to the driver circuits 520 that causes the driver circuits 520 to control the respective driver currents to the LED zones 530, thereby controlling brightness.
The serial communication lines 555 may be utilized in the addressing mode to facilitate assignment of addresses. Here, an addressing signal is sent from the control circuit 510 via the serial communication lines 555 to the first driver circuit 520 in a group of driver circuits 520. The first driver circuit 520 stores an address based on the incoming addressing signal and generates an outgoing addressing signal for outputting to the next driver circuit 520 via the serial communication line 555. The second driver circuit 520 similarly receives the addressing signal from the first driver circuit 520, stores an address based on the incoming addressing signal, and outputs an outgoing addressing signal to the next driver circuit 520. This process continues through the chain of driver circuits 520. The addressing process may be performed in parallel or sequentially for each group of driver circuits 520.
In an example addressing scheme, each driver circuit 520 may receive an address, store the address, increment the address by one or by another fixed amount, and send the incremented address as an outgoing addressing signal to the driver circuit 520 in the group. Alternatively, each driver circuit 520 may receive the address of the prior driver circuit 520, increment the address, store the incremented address, and send the incremented address to the next driver circuit 520. In other embodiments, the driver circuit 520 may generate an address based on the incoming address signal according to a different function (e.g., decrementing).
After addressing, dimming commands may be sent to the driver circuit 520 based on the addresses. For example, during the operational mode, dimming data can be broadcast to a group of driver circuits 520 via the power communication line 565 to configure the duty cycles and provide update signals or other timing information.
In the example shown in
The integrated LED and driver circuit 605 includes the substrate 630 that is mountable on a surface of the PCB interconnect layer 620. The substrate 630 may be, e.g., a silicon (Si) substrate. In other embodiments, the substrate 630 may include various materials, such as gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), aluminum nitride (AlN), sapphire, silicon carbide (SiC), or the like.
The driver circuit layer 640 may be fabricated on a surface of the substrate 630 using silicon transistor processes (e.g., BCD processing). The driver circuit layer 640 may include one or more driver circuits 150 (e.g., a single driver circuit 150 or a group of driver circuits 150 arranged in an array). The interconnect layer 650 may be formed on a surface of the driver circuit layer 640. The interconnect layer 650 may include one or more metal or metal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or any combination thereof. The interconnect layer 650 may include electrical traces to electrically connect the driver circuits 150 in the driver circuit layer 640 to wire bonds 655, which are in turn connected to the control circuit 120 on the PCB 610. In an embodiment, each wire bond 655 provides an electrical connection between the driver circuit 150 or LED zone 140 and the control circuit 120 or other electronic components (e.g., power and ground lines). Additionally, the interconnect layer 650 may provide electrical connections for supplying the driver current between the driver circuit layer 640 and the conductive redistribution layer 660.
In an embodiment, the interconnect layer 650 is not necessarily distinct from the driver circuit layer 640 and these layers 640, 650 may be formed in a single process in which the interconnect layer 650 represents a top surface of the driver circuit layer 640.
The conductive redistribution layer 660 may be formed on a surface of the interconnect layer 650. The conductive redistribution layer 660 may include a metallic grid made of a conductive material, such as Cu, Ag, Au, Al, or the like. The LED layer 670 includes LEDs that are on a surface of the conductive redistribution layer 660. The LED layer 670 may include arrays of LEDs arranged into the LED zones 140 as described above. The conductive redistribution layer 660 provides an electrical connection between the LEDs in the LED layer 670 and the one or more driver circuits in the driver circuit layer 640 for supplying the driver current and provides a mechanical connection securing the LEDs over the substrate 630 such that the LED layer 670 and the conductive redistribution layer 660 are vertically stacked over the driver circuit layer 640.
Thus, in the illustrated circuit 605, the one or more driver circuits 150 and the LED zones 140 including the LEDs are integrated in a single package including a substrate 630 with the LEDs in an LED layer 670 stacked over the driver circuits 150 in the driver circuit layer 640. By stacking the LED layer 670 over the driver circuit layer 640 in this manner, the driver circuits 150 can be distributed in the display area of a display device 100.
In alternative embodiments, the integrated driver and LED circuits 605, 685, 695 may be mounted to a different base such as a glass base instead of the PCB 610.
The PCB 610 includes a connection to a power source supplying power (e.g., VLED) to the LEDs, a control circuit for generating a control signal, generic I/O connections, and a ground (GND) connection. The driver circuit layer 640 includes a plurality of driver circuits (e.g., DC1, DC2, . . . DCn) and a demultiplexer DeMux. The conductive redistribution layer 660 provides electrical connections between the driver circuits and the demultiplexer DeMux in the driver circuit layer 640 to the plurality of LEDs in the LED layer 670. The LED layer 670 includes a plurality of LEDs arranged in rows and columns. In this example implementation, each column of LEDs is electrically connected via the conductive redistribution layer 660 to one driver circuit in the driver circuit layer 640. The electrical connection established between each driver circuit and its respective column of LEDs controls the supply of driver current from the driver circuit to the column. In this embodiment, each diode shown in the LED layer corresponds to an LED zone. Each row of LEDs is electrically connected via the conductive redistribution layer 660 to one output (e.g., VLED_1, VLED_2, . . . VLED_M) of the demultiplexer DeMux in the driver circuit layer 640. The demultiplexer DeMux in the driver circuit layer 640 is connected to a power supply (VLED) and a control signal from the PCB 610. The control signal instructs the demultiplexer DeMux which row or rows of LEDs are to be enabled and supplied with power using the VLED lines. Thus, a particular LED in the LED layer 670 is activated when power (VLED) is supplied on its associated row and the driver current is supplied to its associated column.
Upon reading this disclosure, those of skill in the art will appreciate still additional alternative embodiments through the disclosed principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope described herein.
| Number | Name | Date | Kind |
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| 20210045212 | Lai | Feb 2021 | A1 |
